Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) - USD ($)		9 Months Ended	12 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
Total United States Treasury Bills, cost (in Dollars)		$ 764,376,245	$ 731,902,394	[1]
Total Investments, Percentage of Net Asset Value		110.61%	99.70%
Other Assets Less Liabilities, Percentage of Net Asset Value		(10.61%)	0.30%
Net Assets, Percentage of Net Asset Value		100.00%	100.00%
United States Treasury Bills 0.01% Due 10/01/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.01%
United States Treasury bills, due date		Oct. 01, 2015
United States Treasury Bills 0.01% - 0.02% Due 10/08/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date		Oct. 08, 2015
United States Treasury Bills 0.00% - 0.01% Due 10/15/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date		Oct. 15, 2015
United States Treasury Bills 0.03% Due 10/22/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.03%
United States Treasury bills, due date		Oct. 22, 2015
United States Treasury Bills 0.01% - 0.04% Due 10/29/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date		Oct. 29, 2015
United States Treasury Bills 0.00% - 0.01% Due 12/24/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date		Dec. 24, 2015
United States Treasury Bills 0.02% Due 12/31/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.02%
United States Treasury bills, due date		Dec. 31, 2015
United States Treasury Bills 0.08% Due 01/07/16 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.08%
United States Treasury bills, due date		Jan. 07, 2016
United States Treasury Bills 0.12% - 0.13% Due 01/14/16 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date		Jan. 14, 2016
United States Treasury Bills 0.12% Due 02/04/16 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.12%
United States Treasury bills, due date		Feb. 04, 2016
US Treasury Bill Securities [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
Total United States Treasury Bills, cost (in Dollars)		$ 826,935,744	$ 784,754,985
United States Treasury Bills 0.01% - 0.06% Due 1/08/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date			Jan. 08, 2015
United States Treasury Bills 0.02% - 0.06% Due 1/15/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date			Jan. 15, 2015
United States Treasury Bills 0.06% Due 1/22/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.06%
United States Treasury bills, due date			Jan. 22, 2015
United States Treasury Bills 0.02% - 0.06% Due 1/29/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date			Jan. 29, 2015
United States Treasury Bills 0.01% - 0.06% Due 2/5/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date			Feb. 05, 2015
United States Treasury Bills 0.03% - 0.05% Due 2/12/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date			Feb. 12, 2015
United States Treasury Bills 0.01% - 0.05% Due 2/19/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date			Feb. 19, 2015
United States Treasury Bills 0.03% Due 3/5/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.03%
United States Treasury bills, due date			Mar. 05, 2015
United States Treasury Bills 0.03% - 0.05% Due 3/12/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, due date			Mar. 12, 2015
United States Treasury Bills 0.04% Due 4/16/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.04%
United States Treasury bills, due date			Apr. 16, 2015
United States Treasury Bills 0.07% Due 5/28/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.07%
United States Treasury bills, due date			May 28, 2015
Minimum [Member] | United States Treasury Bills 0.01% - 0.02% Due 10/08/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.01%
Minimum [Member] | United States Treasury Bills 0.00% - 0.01% Due 10/15/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate	[2]	0.00%
Minimum [Member] | United States Treasury Bills 0.01% - 0.04% Due 10/29/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.01%
Minimum [Member] | United States Treasury Bills 0.00% - 0.01% Due 12/24/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate	[2]	0.00%
Minimum [Member] | United States Treasury Bills 0.12% - 0.13% Due 01/14/16 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.12%
Minimum [Member] | United States Treasury Bills 0.01% - 0.06% Due 1/08/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.01%
Minimum [Member] | United States Treasury Bills 0.02% - 0.06% Due 1/15/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.02%
Minimum [Member] | United States Treasury Bills 0.02% - 0.06% Due 1/29/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.02%
Minimum [Member] | United States Treasury Bills 0.01% - 0.06% Due 2/5/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.01%
Minimum [Member] | United States Treasury Bills 0.03% - 0.05% Due 2/12/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.03%
Minimum [Member] | United States Treasury Bills 0.01% - 0.05% Due 2/19/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.01%
Minimum [Member] | United States Treasury Bills 0.03% - 0.05% Due 3/12/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.03%
Maximum [Member] | United States Treasury Bills 0.01% - 0.02% Due 10/08/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.02%
Maximum [Member] | United States Treasury Bills 0.00% - 0.01% Due 10/15/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.01%
Maximum [Member] | United States Treasury Bills 0.01% - 0.04% Due 10/29/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.04%
Maximum [Member] | United States Treasury Bills 0.00% - 0.01% Due 12/24/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.01%
Maximum [Member] | United States Treasury Bills 0.12% - 0.13% Due 01/14/16 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate		0.13%
Maximum [Member] | United States Treasury Bills 0.01% - 0.06% Due 1/08/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.06%
Maximum [Member] | United States Treasury Bills 0.02% - 0.06% Due 1/15/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.06%
Maximum [Member] | United States Treasury Bills 0.02% - 0.06% Due 1/29/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.06%
Maximum [Member] | United States Treasury Bills 0.01% - 0.06% Due 2/5/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.06%
Maximum [Member] | United States Treasury Bills 0.03% - 0.05% Due 2/12/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.05%
Maximum [Member] | United States Treasury Bills 0.01% - 0.05% Due 2/19/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.05%
Maximum [Member] | United States Treasury Bills 0.03% - 0.05% Due 3/12/15 [Member]
Schedules of Investments (Unaudited) (Details) - Investments (Parentheticals) [Line Items]
United States Treasury bills, effective rate			0.05%

[1] Previously reported as "Statements of Financial Condition." Please refer to Note 2A.

[2] Rounds to less than 0.01%